1. Field of the Invention
This invention relates generally to mechanical locksets employed to secure doors. More particularly, the present invention relates generally to a mortise-type lockset that incorporates an internal clutch assembly.
2. Description of the Related Art
Recent hardware trends and the Americans with Disabilities Act requirements for lever handles at both exterior and interior sides of doors have focused the market on lever operated lock mechanisms. Because both intruders and users can impose greater forces on the lock mechanism having lever operating systems, it is particularly important to provide a mechanism that is not vulnerable to being compromised intentionally or otherwise. In some cases lever operated lock mechanisms have included a mechanical clutch mounted between the operator or operating handle and the lockset. Such clutches selectively mechanically couple the operating handle to the lockset and permit rotation of the operating handle to retract the latch or bolt and allow entry through the doorway.
An example of an electromechanical type of clutch may be found in U.S. Pat. No. 5,640,863. Such separate, add on clutches work well and have the advantage of being compatible with existing locksets, allowing existing key-based security systems to be retrofitted with electronic security capabilities. Purely mechanical clutch assemblies are typically used between a handle or operator and the bolt of a lockset. Typically, if the door is locked either with a thumb turn or a key, the clutch assembly uncouples the mechanical connection between the operator and the bolt. Thus, an intruder who attempts to use brute force to turn the operating handle will realize that no amount of force will withdraw the bolt and allow entry through the doorway secured by the lockset.
In some cases known clutch mechanisms have been vulnerable, particularly after years of service, due to wearing of the individual parts thereof. This may lead to mechanisms that jam and become inoperative. In some cases, however, wear of the components may result in malfunctions such as jamming or make the assembly inoperative and prevent access to the secured side of the door or even prevent egress from the secured side to the unsecured side.
Briefly stated, the invention in a preferred form is a lockset which includes a housing and a latch extending from the housing. The latch has an extended position and a retracted position. The mechanism includes apparatus for biasing the latch to the extended position, apparatus for defining a locked mode and an unlocked mode, and apparatus for transferring an operator input motion to move the latch to the retracted position in the unlocked mode. The apparatus for transferring includes a locking piece, a cam surface and a cam follower. A spring biases the cam follower in a first direction toward the cam surface and a second spring provides an override movement of the locking piece to thereby compensate for any off-center relationship between the rotation axis of the follower and the cam surface and to prevent jamming of the locking piece.
The first and second springs are coil springs disposed in coaxial relationship. The second coil spring has a higher spring rate than the spring rate of the first coil spring. The first and second coil springs may be disposed in coaxial relationship with a pin of the cam follower. The locking piece receives the pin and has a cup-shaped portion which may be disposed in generally coaxial relationship with the first and second coil springs to form a retainer flange for the second coil spring. The retainer flange is disposed intermediate axial extremities of the first coil spring and the second coil spring.
An object of the invention is to provide a lock mechanism that will minimize the risk of jamming of the mechanism despite repeated use of the mechanism for a very large number of duty cycles.
Another object of the invention is to provide a lock mechanism that will function consistently to self compensate for liberal manufacturing tolerances, assembly misalignment, wear and/or extreme forces applied to the mechanism.
These and other objects, features and advantages of the invention will become readily apparent to those skilled in the art upon reading the specification in conjunction with the accompanying drawings.